Membrane fluxes, bypass flows, and sodium stress in rice: the influence of silicon

Silicon reduces rice shoot sodium accumulation by blocking transpirational bypass flow or increasing shoot growth, but does not affect transmembrane Na+ fluxes or the rapid Na+ influx-efflux cycle in roots. Abstract Provision of silicon (Si) to roots of rice (Oryza sativa L.) can alleviate salt stre...

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Bibliographic Details
Published in:Journal of experimental botany 2018-03, Vol.69 (7), p.1679-1692
Main Authors: Flam-Shepherd, Rubens, Huynh, Wayne Q, Coskun, Devrim, Hamam, Ahmed M, Britto, Dev T, Kronzucker, Herbert J
Format: Article
Language:English
Subjects:
Biological Transport
Cell Membrane - metabolism
Oryza - physiology
Plant Transpiration
Research Papers
Salt Tolerance
Silicon - metabolism
Sodium Radioisotopes - metabolism
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Summary:Silicon reduces rice shoot sodium accumulation by blocking transpirational bypass flow or increasing shoot growth, but does not affect transmembrane Na+ fluxes or the rapid Na+ influx-efflux cycle in roots. Abstract Provision of silicon (Si) to roots of rice (Oryza sativa L.) can alleviate salt stress by blocking apoplastic, transpirational bypass flow of Na+ from root to shoot. However, little is known about how Si affects Na+ fluxes across cell membranes. Here, we measured radiotracer fluxes of 24Na+, plasma membrane depolarization, tissue ion accumulation, and transpirational bypass flow, to examine the influence of Si on Na+ transport patterns in hydroponically grown, salt-sensitive (cv. IR29) and salt-tolerant (cv. Pokkali) rice. Si increased growth and lowered [Na+] in shoots of both cultivars, with minor effects in roots; neither root nor shoot [K+] were affected. In IR29, Si lowered shoot [Na+] via a large reduction in bypass flow, while in Pokkali, where bypass flow was small and not affected by Si, this was achieved mainly via a growth dilution of shoot Na+. Si had no effect on unidirectional 24Na+ fluxes (influx and efflux), or on Na+-stimulated plasma-membrane depolarization, in either IR29 or Pokkali. We conclude that, while Si can reduce Na+ translocation via bypass flow in some (but not all) rice cultivars, it does not affect unidirectional Na+ transport or Na+ cycling in roots, either across root cell membranes or within the bulk root apoplast.
ISSN:0022-0957
1460-2431
DOI:10.1093/jxb/erx460